Cardiac monitoring system and method

ABSTRACT

A cardiac monitoring method and system provides advanced ischemia and infarction analysis and monitoring. Advanced calculations are performed on ECG signals to obtain parameter values relating to myocardial ischemia and infarction. Dominant heart beats are averaged to form a smooth beat, which is analyzed to determine the parameter values continuously and in real-time. The result of each analyzed time interval is presented as points in a trend graph on a monitoring display. All calculations are performed on-line and the trend curves are updated immediately. Systems and methods for monitoring, analyzing, and/or diagnosing cardiac activity that display a state of signals received from leads attached to a patient on a graphic depiction of the patient are also provided. The graphic depiction of the patient may include electrode position information.

This application is a continuation-in-part application of U.S. Ser. No.08/320,511, filed Oct. 7, 1994 now U.S. Pat. No. 5,520,191.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to cardiac monitoring systems and, moreparticularly, to cardiac monitoring systems which provide an analysisand display of parameters relating to the condition of ischemicpatients. The invention also relates to systems and methods formonitoring, analyzing, diagnosing, and/or receiving radiotransmissionsrelating to cardiac activity and displaying a state of signals receivedfrom leads attached to a patient on a graphic depiction of the patient.

(2) Description of the Related Art

A number of new clog dissolving agents presented by the pharmaceuticalindustry during the past couple of years have given cardiologists theability to immediately treat acute myocardial ischemia through chemicalthrombolytic therapy. However, it is frequently difficult to properlycontrol and adjust such therapy during the acute phase of a myocardialischemia. Known methods are either expensive or have too large a delay(up to several hours) between the time of the myocardial ischemia timeand the presentation of the results. Some cardiac monitoring systems andmethods also utilize a known 12-lead ECG in which ECG signals aredisplayed directly on a monitor in real-time. Such a 12-lead ECGarrangement has the disadvantages that a large number of electrodes mustbe placed on the patient in positions which cover mainly the frontalparts of the myocardium. A large storage capacity is also required inorder to record all the ECG signals from the electrodes. However, manydoctors are familiar with the format of the 12-lead ECG.

SUMMARY OF THE INVENTION

The present invention constitutes a substantial improvement in cardiacmonitoring systems, and in particular, an improvement in cardiacmonitoring systems providing an analysis and display of parametersrelating to the condition of ischemic patients. It is an object of thepresent invention to overcome the aforementioned disadvantages of knowncardiac monitoring systems. In particular, it is an object of thepresent invention to provide real time parameters describing the acutecondition of the myocardium during thrombolytic therapy in the initialphase of myocardial infarctions.

Further, it is an object of the present invention to provide a cardiacmonitoring system in which the ECG signals are represented by threeperpendicular leads which are continuously averaged and stored in equalintervals and then later displayed in the format of a derived standard12-lead ECG.

It is also an object of the invention to continuously store the threeperpendicular leads, X, Y and Z, and recalculate the signals therefromin order display a derived standard 12-lead ECG in real-time.

It is also an object of the invention to provide an improved method tobe used in pharmaceutical studies to verify the actual benefits of newdrugs.

It is a further object of the invention to provide an improvedmonitoring method to be used during different kinds of coronaryoperations, such as PTCA--coronary artery balloon dilatation, or otherprocedures requiring an accurate real-time analysis and monitoring.

It is a further object of the invention to provide cardiac monitoringsystems and methods that display a state of signals received from leadsattached to a patient on a graphic depiction of the patient.

The method in a preferred embodiment of the present invention presentsthe required information in real-time using advanced calculations on ECGsignals to obtain "simple" parameter values describing the myocardialischemia (lack of oxygen) and the course of infarction. Eight standardECG surface electrodes are placed on the patient according to the Frankelectrode system developed in the 1940s. The signals in the eight leadsare processed in a known manner to form the ECG vector which can bedescribed by three perpendicular leads: X, Y, and Z. These three leadscontain all the information necessary to describe the ECG completely.

ECG changes are continuously analyzed to reflect the course of ischemiaand infarction based on vector-cardiography. All dominant beats arecontinuously acquired for the analysis and averaged at even intervals toform one very smooth beat, suitable for high definition calculations.Those intervals may range from ten seconds up to four minutes. The firstaveraged beat is used as an initial reference beat. All succeeding,averaged beats will be compared to this initial beat to plot thechanges.

The resulting, averaged beat is analyzed to form a plurality ofparameters. The ST vector magnitude (ST-VM) measures the offset of theST-segment and is commonly accepted as a measure of ischemia in themyocardium. The change of the ST magnitude compared to the initialreference beat (when monitoring was started) (STC-VM) is alsocalculated. The QRS vector difference (QRS-VD) measures changes in theQRS complex compared to the initial ECG and reflects the change inmorphology of the QRS complex compared to when monitoring was started.The QRS-VD parameter has been linked to the course of the myocardialinfarction in several studies.

The invention displays the result of the advanced analysis from everytime interval as a new point in very simple trend graphs that arecontinuously updated. All calculations are performed online so the trendcurves are updated immediately. The fundamental advantage of this methodis that every complex and subtle information from the ECG signals isanalyzed and processed to finally form simple parameter values which aredisplayed in simple trends. Since the result is presented in the simplegraphical form of a trend over time, it is perfect for on-linemonitoring and the trend curves provide immediate information on thedegree of ischemia or the course of an ischemia. A change in thecondition of the heart may even be visible on the display before thepatient undergoes pain.

Since the average ECG is always stored, the original ECG of every pointof the trend curve may always be displayed as either a derived 12-leadECG, the X, Y and Z leads, vector magnitude or vector loops. When apatient is monitored, the acquired information is permanently stored inthe central workstation of the system. The information may be copiedonto recording media, such as a 3.5" floppy disk, and subsequentlyanalyzed for clinical or scientific purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation illustrating the QRS-VD parameter.

FIG. 2 is a graphical representation illustrating the ST-VM parameter.

FIG. 3 is a graphical representation illustrating the STC-VM parameter.

FIG. 4 is a flowchart depicting the manner in which three perpendicularleads (X, Y, and Z) are produced in a preferred embodiment of theinvention.

FIG. 5 is a flowchart showing the initial steps in the analysis andmonitoring used in the preferred embodiment of the invention.

FIG. 6 is a flowchart depicting the manner in which the averaged beat,represented by the averaged X, Y and Z leads, undergoes advancedcalculations to determine parameters describing the condition of theECG.

FIG. 7 is a diagram illustrating elements of the system in a firstembodiment of the invention.

FIG. 8 is a block diagram graphically illustrating the connection of thecentral workstation to other components of an apparatus employing theinvention.

FIG. 9 is a diagram showing the top part of a graphical interfacedisplay which appears on the central workstation of a system employingthe invention.

FIG. 10 is a diagram showing an example of the display format used formonitoring each patient on a central monitoring unit.

FIG. 11 shows the front face of a bedside monitor used in a firstembodiment of a system employing the invention.

FIG. 12 shows the front face of an acquisition module used in anotherembodiment of a system employing the invention.

FIG. 13 shows the overall input/output possibilities in an apparatusemploying the invention.

FIG. 14 shows an example of a single page printout, having a pluralityof ECG signals printed under each other, produced by the invention.

FIG. 15 shows a the display of a patient's torso on a display devicealong with electrode status indicator lights and annunciator means.

FIG. 16 shows the placement of a 3-lead electrode leadset on a patient'storso.

FIG. 17 shows the placement of a 3-lead electrode leadset on a patient'storso for paced patients.

FIG. 18 shows the placement of a 3-lead electrode leadset on an infant.

FIG. 19 shows the placement of a 4-lead electrode leadset on a patient'storso.

FIG. 20 shows the placement of a 4-lead electrode leadset on a patient'slimbs.

FIG. 21 shows the placement of a 5-lead electrode leadset on a patient'storso for monitoring.

FIG. 22 shows the placement of a 5-lead electrode leadset on a patient'storso for holter recording.

FIG. 23 shows the placement of a 5-lead electrode leadset on a patientaccording to the EASI leadset.

FIG. 24 shows the placement of a 7-lead electrode leadset on a patient'storso for late potential analysis.

FIG. 25 shows the placement of an 8-lead electrode leadset on apatient's torso according to Frank.

FIG. 26 shows the placement of a 10-lead electrode leadset on apatient's torso to get true 12-lead ECG (RA and LA may be placed onarms, RL and LL further down on legs).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 7 shows the setup of the system in a first embodiment of a systemutilizing the invention. It consists of at least one central monitoringunit 10, a central workstation 11 for controlling the system, includingthe display on the central monitoring unit(s), and for storing data, alaser printer 12 and a plurality of bedside monitors 13, one for eachpatient. All of the units communicate via an Ethernet network 14.

Processing functions are divided between central workstation 11 and eachbedside monitor 13. The distributed intelligence ensures maximum systemreliability and offers both powerful traditional monitoring and advancedischemia monitoring.

Each of the bedside monitors 13 combines multilead arrhythmia analysiswith new, advanced ischemia monitoring features and does all thecalculations for the ECG analysis, presents the information on thedisplay and transmits it over Ethernet network 14 to a centralprocessing unit in the workstation 11. FIG. 12 shows the front face ofan exemplary bedside monitor 13. In addition to the ECG analysis, eachbedside monitor 13 is also available with a number of options, such asnon-invasive blood pressure, pulse oximetry, dual invasive pressures anddual temperatures, and is operated simply by touching theself-instructive menus on the front of the monitor. Analogue ECG outputson the back of the bedside 15 monitors allow connection to other medicalequipment.

Eight ECG leads are used for improved sensitivity of the analysis ofboth arrhythmias and ischemia. With information from all eight leads,the ischemia analysis is able to reflect ischemic changes from theentire myocardium. The ischemic evolution over time is presented in atrend graph that is continuously updated on the display. The trend graphmay include up to 8 days of continuous monitoring. With four traces anda trend graph, a waveform may be displayed for every physiologicalparameter in addition to the vital trend graphs. (For patients withoutischemic symptoms, 4 leads can be used for monitoring.) The averagedbeats in the form of the X, Y and Z leads are automatically calculatedand stored every minute. From these signals a derived 12-lead ECG may bereviewed on the bedside monitor at any time during the monitoringsession.

The central workstation can automatically identify up to six differentfunctions (MIDA, HR/PVC, spo², NIBP, IBP and Temp for example) in eachbedside monitor and all of the physiological information acquired by thebedside monitors can be transferred for examination and storage at theworkstation. The monitoring functions controllable by the centralworkstation will thus vary depending on the configuration of the bedsidemonitors connected to the central workstation. For example, centralworkstation 11 may provide conventional ECG monitoring, arrhythmiamonitoring, ischemia monitoring with parameters reflecting the ECGchanges in clear trend graphs, averaged derived 12-lead ECG display,24-hour full disclosure arrhythmia of all monitored patients, 24-hourcontinuous 12-lead ECG display derived from the continuously stored X,Y, and Z leads for all monitored patients and monitoring of any and allnon-ECG functions monitored on the bedside monitors such as spo², NIBP,BP and Temp.

The central workstation is preferably a networking personal computeroperating with specialized menu-driven applications software. Anexemplary connection of the central workstation to other components isshown in FIG. 8 and an exemplary illustration of the functions which maybe performed is shown in FIG. 13. The central workstation provides astraightforward and simple user interface operated through the selectionof "keys" in a graphical display. Each key has an instructive text orsymbol describing the function of the key. A mouse (or other pointingdevice) is used to point to and select a desired key. (In the examiningfunctions, the mouse is also used to point out the ECGs to be enlarged,etc.) The surface of a key is normally grey. However, active keys aremade yellow and void keys that cannot be accessed are dark grey.

FIG. 9 shows an example of the initial menu displayed in an upperportion of the display in a preferred embodiment of the invention. Thereare two rows of keys. The keys in the top row are labeled with numberscorresponding to each one of a number of patients, System, Signal Statusand Stored Patients. The lower row of keys preferably contains keycommands for examining a patient file. For example, the keys may belabeled as Patient Info, Alarm, Report, Trend, ECG & VCG, ArrhythmiaEvents, ECG MIDA, ECG Review, All Leads and Setup. The keys are used toselect and control all functions, both on the central monitors and onthe workstation itself.

Signal status messages are displayed on the display of the workstationif no central monitor is in use. (Otherwise, signal status messages arealways displayed on the central monitor.) A red patient key is used toindicate that something is wrong, that there is bad signal quality orproblem with the analysis or other errors. If so, the reason may be seenin the Signal Status function. A crossed over key is used to indicatethat the analysis has paused. The actual message for a specific patientis then displayed to the right of the patient name in the upper part ofthe workstation display.

CENTRAL MONITORING UNITS

All parameters available to the central workstation may be displayed astrend graphs on one or more central monitoring units 10. The centralmonitoring unit(s) 10 display the "live" situation of a plurality ofpatients simultaneously. The central monitoring units are preferablylarge (e.g., 17- or 21-inch), high-resolution computer monitors such asthat shown in FIG. 7. Software display drivers in the workstationutilize high resolution graphics and the display is preferably at least1024×768 pixels resolution. The monitors may continuously andsimultaneously monitor ECG waveforms, vital parameters, alarms and vitalischemia trendings for each of a number of patients.

Arrhythmia alarms are presented in red letters on the displays and a24-hour full disclosure arrhythmia review function offers completecontrol and documentation of all arrhythmias. The central monitoringunit(s) 10 also enable examination of derived 12-lead ECGs of everyminute monitored. All other functions are displayed and controlled onworkstation.

The information on the monitors is fixed in order to always present thecurrent status of all patients. All interactive functions andexamination of patient data which appears on the monitors is controlledfrom the workstation. The left half of the monitor screen presentsconventional monitoring including heart rates and patient information,waveforms, arrhythmia alarms and optional vital signs while theright-hand side presents the ischemia trends. The graphs display theischemic evolution of each monitored patient starting from a designatedtime, such as the patient's admission. The graphs are continuouslyupdated to always include the most recent values. Up to six patients maybe monitored on each display. When more than four patients aremonitored, additional monitors may be used. The network 14 allows theselection of any two waveforms from each bedside patient monitor to bedisplayed on the central monitor. The waveform selected to be displayedon the central monitor need not be the same waveform selected fordisplay on the corresponding bedside monitor 13. An example of a trendgraph displayed on the central monitor for a single patient is shown inFIG. 10. The signal status and MIDA messages are identical to the onesdisplayed in the Signal Status overview of the display for the centralworkstation discussed later.

The content of the display of a respective patient on the centralmonitors (leads, filters, size and speed) is selected by centralworkstation 11 in the manner described below. The same information isalways displayed at the same location in the display for improvedfunctionality. The left side of the display contains bed number 101,patient name 102, heart rate 103, pacemaker information 104 and signalstatus message 105. The right side of the display contains trendgraph(s) 106 and MIDA recording status message 107.

A patient is chosen for monitoring by clicking the number keycorresponding to the patient in the top row of keys on the Workstation.

The Setup Menu key is selected to adjust the patient's display. If theMonitored ECG Lead key of the Setup Menu is selected, then a picture isdisplayed which contains the waveform for each of the patient leadsalong with a respective corresponding key, as well as keys for selectingthe filtering, curve size and sweep speed of the displayed waveforms. Ifwaveforms other than ECG leads, such as Spo2 and PA pressure, aremonitored, then these appear in the display as well and are controlledin the same manner as the ECG leads. The primary waveform to bedisplayed on the central monitor is selected by clicking thecorresponding key.

The setup menu in the first embodiment displays three filter keys whichenable the displayed waveform to be filtered for improved visualimpression. The first key, "None", displays the waveform unfiltered. Thesecond key is labeled "0.05-100 Hz" and gently filters the curve frombaseline variations below 0.05 Hz and noise above 100 Hz. The third keyis labeled "0.5-40 Hz" and filters the displayed curve from baselinevariations below 0.5 Hz and noise above 40 Hz. The setup menu in thepreferred embodiment also displays three ECG size keys which set thesize of the displayed waveform. When the "Auto" key is selected, thesize of the displayed curve is continuously adopted to fill two thirdsof the height available for the curve. The adoption is very slow so thatif the original amplitude of the curve slowly decreases (maybe due tonecrosis), the automatic adoption may result in an unaffected curve onthe monitor. The "10 mm/mV" key sets the amplitude of the displayedcurve to 10 mm/mV. The "20 mm/mV" key sets the amplitude of thedisplayed curve to 20 mm/mV.

All curves on the central monitor have the same speed. The speed may beset to 25 mm/sec or 50 mm/sec via selection of the appropriate key.

For all patients, a second monitoring curve (additional ECG,pulseoximetry or pressure) may also be selected for display in additionto the primary curve. This function is controlled by selection of a keymarked "On/Off" which appears under the header "2nd wave" in the setupmenu display. Selecting the On/Off key activates the second curve. A keymarked "Wave 1" is selected to enable control of the upper curve (lead,filter, etc.). A key marked "Wave 2" is selected to enable control ofthe lower curve.

The Patient Info key allows inputting of the patient's name, ID,original symptoms and physician comments. The information is entered onrespective lines using the keyboard in typewriter fashion and thenpressing the enter key. The Patient Info menu also contains a Pacemakerkey which is selected to indicate that the patient has a pacemaker.

The menu also has an Add note feature which permits the entering ofnotes and observations at the workstation at any time. When the Add notekey is selected, a field is opened at the bottom of the display, thetime is automatically displayed, and the Add note key is changed to asave note key. The text of the note is entered and edited using thekeyboard.

The note is saved by clicking on the Save Note key. If the patient'swaveforms are stored for subsequent analysis, the system stores allnotes as well. They may be reviewed and printed on paper at any time.

The Patient Info menu is closed by selecting either a Save Patient Infokey or a Cancel key. When a patient is discharged from the bedsidemonitor, the central workstation stores all recordings, including24-hour full disclosure arrhythmia, by default until the storagecapacity is needed for new recordings. When capacity is full, the oldestrecordings will be erased automatically.

Once the patient has been entered into system as described aboved andthe display for he central monitor has been formatted as describedabove, the system then commences on-line myocardial ischemia dynamicanalysis and monitoring (MIDA) for treating patients with myocardialinfarction, unstable angina or when monitoring patients during andpost-PTCA.

Based on the electrical signals from eight ordinary surface ECGelectrodes placed according to Frank, three perpendicular leads (X, Y,and Z) are produced in the manner shown in FIG. 4. The method used inthe system permits ischemia monitoring based on Frank leads, analyzingthe X, Y, and Z signals to achieve unique parameters, such as ST-VM,QRS-VD and STC-VM, which are displayed in a trend chart.

When monitoring starts in the manner shown in FIG. 5, beats undergo amorphological classification and a morphological template is defined. Ifa beat fits the morphological template, a match template is built, suchby selecting a normal ECG beat to serve as the template. Beats arecompared to the match template to determine which beats are "normal"beats that should be included in the analysis and which beats should beexcluded from the MIDA analysis. During the remainder of the analysis,the three leads X, Y and Z are continuously scanned for "normal" beats.When a normal beat is found, it is matched and included in an average ofthe acquired normal beats formed at even time intervals, preferablyevery minute provided that the quality of the signal is sufficient. TheECG from the first average beat is referred to as the Reference Complexand used as a reference to which the ECGs from all subsequent beats arecompared to see the relative change over time.

At even time intervals between a range of 10 seconds and 4 minutes, theaveraged beat, represented by the averaged X, Y and Z leads, undergoesadvanced calculations as shown in FIG. 6 to determine up to thirtydifferent parameters describing the condition of the ECG. The parametersare stored in addition to the 5 averaged ECG itself.

There are two kinds of parameters: absolute and relative. Absoluteparameters are calculated from the actual ECG complex itself. Relativeparameters are calculated from the difference between the current ECGcomplex and the initial reference complex to reflect serial changes overtime.

The following are examples of absolute parameters: QRSmax, QRSmean,ST-VM, ST-VM2, X-ST, Y-ST, Z-ST, QRS-SPA, HR, QRtime, QStime, QTtime,RRtime, T-VM, T-Az, T-El, X-ST, Y-ST, Z-ST and Abnorm.

QRSmax (mV) is the maximum magnitude within the QRS-complex.

QRSmean (mV) is the mean magnitude of the ECG-vector during the timeranging from QRS onset up to QRS end of the initial QRS-complex.

The ST vector magnitude (ST-VM) measures the total offset of theST-segment and is commonly accepted as a measure of ischemia in themyocardium during ischemia. It is measured in every averaged beat, 60milliseconds after the J point (the end of the QRS complex). The valuesfrom the X, Y and Z leads are fed into the formula: ##EQU1## and theresulting ST-VM value is plotted in the trend graph. The way the formulais constructed, an ST elevation in one lead does not neutralize an STdepression in another lead. Both elevations and depressions are detectedsimultaneously. See FIG. 2. Since the ST segment is measured in both theX, Y and Z leads, it provides one ST measure that covers the entireheart.

ST-VM2 (mV) is the ST vector magnitude 20 ms after the J point.

X-ST (mV) is the ST level in the X lead 60 ms after the J point.

Y-ST (mV) is the ST level in the Y lead 60 ms after the J point.

Z-ST (mV) is the ST level in the Z lead 60 ms after the J point.

QRS-SPA (nanV²) is the area in the space drawn by the ECG-vector fromthe point of the initial QRS onset to QRS end. HR (beats per minute) isthe mean value of the heart rate during the MIDA interval.

QRtime (ms) is the time between QRS onset and the maximum magnitude ofthe current complex.

QStime (ms) is the time between QRS onset and QRS end of the currentcomplex.

QTtime (ms) is the time between QRS onset and the maximum magnitudewithin the T wave of the current complex.

RRtime (ms) is the mean value of the RR intervals during the averagingperiod.

The T vector magnitude (T-VM) measures the maximum magnitude within theT-wave of the current complex in mV. The ECG-vector in this point iscalled the T-vector.

T-Az is the angle of the T-vector in the transversal plane, 0 to 180degrees from sinister to dexter, and positive if anterior and negativeif posterior.

T-El is the angle of the T-vector from the vertical axes, 0 to 180degrees from dist to cranium.

Abnorm is the number of abnormal beats during the averaging period. Allbeats that are not classified into the reference class are labelledabnormal.

The change of the ST magnitude compared to when monitoring was 15started (STC-VM) is also calculated as shown in FIG. 3. The STdifferences are fed into the formula: ##EQU2##

The following are examples of relative parameters: QRS-VD, QRSI-VD,QRSA-VA, QRSC-VM, STC-VA, STC-VM, TC-VA and TC-VM. The QRS vectordifference (QRS-VD) measures changes in the QRS complex compared to theinitial ECG and reflects the change in morphology of the QRS complexcaused by, e.g. necrosis and temporary ischemia compared to whenmonitoring was started. The complex is compared to the initial QRScomplex and the arial difference (A_(x) in FIG. 1) is calculated in theX, Y and Z leads.

The values are fed to the formula: ##EQU3## and the resulting QRS-VD isplotted in the trend graph.

QRSI-VD (mVs) is the initial QRS vector difference which is the same asfor QRS-VD except that the areas A_(x), A_(y) and A_(z) range from QRSonset of the initial QRS complex and 40 ms forward.

QRSC-VA is the QRS vector angle change and represents the change in theangle between the current and initial QRS vectors.

QRSC-VM (mV) is the QRS vector magnitude change and represents thedistance between the initial and current QRS vectors.

STC-VA is the ST vector angle change and represents the change in theangle between the initial and current ST vectors.

STC-VM (mV) is the ST vector magnitude change and represents thedistance between the initial and current ST vectors.

TC-VA is the T vector angle change and represents the change in theangle between the initial T-vector and the current T-vector.

TC-VM (mV) is the T vector magnitude change and represents the distancebetween the initial and current T-vectors.

Selected ones of the relative and absolute parameters describing thecourse of the ischemia may be chosen for display and plotted in a trendgraph. The three most common are the QRS-VD (morphological changes) andST-VM (st-measurements) and STC-VM (st changes).

The averaged ECG that is stored at the end of each time intervalcontains the values for each of the X, Y, and Z leads. Since the X, Y,and Z contains all information of the ECG, it may also be used tocalculate a full 12-lead ECG in real time using a known algorithm. Thisway, the preferred embodiment may also continuously display a calculatedaveraged 12-lead ECG for every minute during the entire monitoringperiod of up to 48 hours in the format of a 12-lead ECG on centralworkstation 11. Based on the continuously stored X, Y and Z leads, acontinuous calculated 12 lead ECG could also be displayed next to achart with the occurrence of arrhythmias over a selectable range ofhours marked as colored bars. The preferred embodiment may also producea single page printout with a plurality of 12-lead ECG signals printedunder each other. See, for example, FIG. 14. The MIDA trends for eachpatient may be examined in detail one at a time on the workstationdisplay. The trends of all patients may be monitored continuously on thecentral monitor using the format shown in FIG. 10.

Depending on the amount of memory provided, the MIDA recording may last,for example, only approximately 48 hours at one-minute intervals. Afterthat, the memory is full and the recording is automatically stopped.Below is an exemplary chart comparing MIDA time intervals to maximumlength of the recording.

    ______________________________________                                        MIDA Time Interval                                                                             Maximum Length of Recording                                  ______________________________________                                        10 seconds       8 hours                                                      15 seconds       12 hours                                                     30 seconds       24 hours                                                     1 minute         48 hours (two days)                                          2 minutes        96 hours (four days)                                         4 minutes        192 hours (eight days)                                       ______________________________________                                    

The arrhythmia full disclosure works differently, always keeping themost recent 24 hours in memory.

The setup menu contains a MIDA Relearn key to control the MIDA method.When the MIDA Relearn key is selected, the workstation display shows thelatest ECG signals acquired with beat labels (beat labels are updatedapproximately 30 seconds). Every detected QRS complex is labelled withan "M" if it is recognized as a MIDA type of beat (matches the MIDAtemplate). The present MIDA Reference Complex is displayed to the leftof the 20 waveforms as scaler X, Y and Z leads. This is the actual,initial, averaged beat to which all subsequent beats will be comparedwhen calculating the relative trend parameters.

The system provides a Restart MIDA key in the MIDA setup display forbeginning the process over again. If the Restart MIDA key is selected, awarning message is displayed with options to cancel (No/Cancel) orproceed (Yes). Then a message "Selecting MIDA template, please wait for20 seconds" is displayed with an option to cancel.

If the process is not cancelled, a suggested new template is displayedin a square for consideration by the user along with three keys forselection. If the Yes key is selected, the entire previous MIDArecording is erased, the suggested template is accepted and the methodis restarted. The display is reset, but with no MIDA Reference Complexdisplayed, since no new Reference Complex has yet been formed. If the Nokey is selected, the template selection procedure is restarted and amessage asking the user to wait for 20 seconds is displayed.

The MIDA system also includes a "MIDA Relearn" feature, the steps ofwhich are identical to the Restart MIDA command described above exceptthat the previously recorded and stored data is not erased.

This feature is appropriate when the MIDA analysis is no longer capableof tracking the ECG. MIDA relearn will find a new template for includingECG complexes in the analysis. (ECG changes always refer to the initial,reference ECG.)

The system also permits the user to review the MIDA Signal Status 107included in the display, shown in FIG. 10, for each patient. The signalstatus for all patients is displayed in a Signal Status table when theSignal Status key in FIG. 9 is selected. Below is a list of differentpossible MIDA signal status messages in order of priority. The line withmessage of highest priority is indicated with a red background.

1) No MIDA Recording possible with current patient cable. An 8-leadcable is needed for the MIDA recording. If a 5-lead cable is in use,this message is shown.

2) MIDA Recording Ended. The MIDA Recording may last for a maximum of 48hours with one-minute intervals. When memory is full, the recording isautomatically stopped and this message is shown.

3) No MIDA Recording due to Spikes on signal. A signal spike is a veryshort disturbance of considerable signal strength. The orgin of thedisturbance may be pacemaker spikes, bad lead wires or electromagneticradiation from other equipment. The system will automatically turn thespike filter off if the patient has got a pacemaker, as indicated in thePatient Info function.

4) No MIDA Recording due to Noisy Signal. Noise may be caused by manyreasons. Bad patient electrode connection may be one reason. Linedisturbances from other equipment close to the patient cable may beanother.

5) No MIDA Recording due to Baseline Drift. If the baseline drift is toobig, this may distort the ECG. To prevent this, the MIDA Recording ishalted. (Baseline drift is a variation in the offset voltage)

6) No MIDA Recording due to lead fail. One of the ECG leads is notworking properly.

7) No MIDA Recording due to no reference type of beats. This message isactive if the minimum number of reference type of beats was not receivedduring the previous MIDA interval.

In another embodiment of the invention shown in FIG. 15, a graphicaldepiction of at least part of the patient 150 is provided and statussignal lights 152 corresponding to each electrode connected to thepatient are disposed on the graphical depiction 150. Further, statusannunciator means 154 corresponding to each electrode, which may providealphanumeric output, may be provided for indicating the status of eachelectrode. The status of each electrode (whether a MIDA test is beingdone or not) may be one of conditions 3, 4, and 5 discussed above, forexample. In addition, the status annunciator means may indicate that anelectrode has failed, is not properly connected to the body, or in facthas even fallen off, which conditions are manifested as a high electrodeimpedance. Further, the impedance itself may be displayed by the statusannunciator means. The status signal lights may blink to call attentionto the status annunciator means and to pinpoint to which electrode(s)the information conveyed by the status annunciator means are directed.The display may be any suitable means, such as a CRT (color ormonochrome), active LCD (TFT), passive LCD (SDN), plasma,electroluminescent (EL), or ferro LCD, for example. The display may alsobe produced by a projector.

The system may also utilize a back position sensor. Since the heart isrelatively mobile in the chest, it is only natural that it changesposition within the chest when the patient changes position in the bed,e.g. from lying on the back to lying on the side. Since the electrodesrecord the electrical activity on the surface of the chest, the movementresults in a change in the ECG. The influence of this change affectseach of the MIDA parameters differently. Since ST-VM measures thestrength of the ST deviation, regardless of direction, it is lesssensitive than other "ordinary" ST measurements. The parameter QRS-VDis, however, very sensitive to these changes. A back position sensormakes it possible to tell if a change in the trend was caused by changeof body position or not.

The Back Position Sensor connects to the junction block of the 8-leadECG cable. The information from the back position sensor is recorded anddisplayed on a separate line below the trend graph. This line may havethree colors indicating the following states:

    ______________________________________                                        Color             State                                                       ______________________________________                                        Green             On Back                                                     Yellow            Not On Back                                                 Grey              No Trend available                                          ______________________________________                                    

The MIDA trend may be displayed on the central monitor as describedpreviously. The Trend key also arranges for the picture to be displayedon the display of the workstation for review.

Keys appear to the left allowing the user to select what trend will bedisplayed. These keys may be labelled MIDA and HR/PVC. Up to fourdifferent trend curves may be displayed in the trend graph. To be ableto tell the curves apart, they are displayed in different colors. Thename of each trend curve is 5 also written over the graph in the samecolor as the curve itself.

The system provides a cursor, controlled by the mouse, in order to, forexample, mark points of special interest. (If points of special interestare marked in the trend curve, they may be of assistance when examiningthe corresponding 12-lead ECGS.) By pointing and clicking in the trend,the cursor is moved to the desired time. Alternatively, the cursor maybe moved step by step by pressing the right and left arrows under Cursorlabels on the bottom of the display of the trend graph. The systemdisplays time of the trend graph corresponding to the position of thecursor on the top of the graph, both as time of day and time sinceadmission. The system also displays the exact values of the parametersto the left and to the right of the time.

Points are marked by placing the trend cursor at the desired time andselecting the check key which is displayed between the arrows under theMark label to the right under the graph. When the trend cursor is placedon a marked time, the system turns the check key to yellow.

The user can jump directly between separately marked times by selectingthe right and left arrows under the Mark label. The system unmarks atime whenever the user presses the check key again.

The system also permits the user to change the parameters in the trendgraph. (Users normally select the QRS-VD and ST-VM6 parameters fordisplay in the trend graph. The MIDA analysis includes thirty parametersthat are continuously calculated and stored.) The MIDA trend displaycontains keys under the Trend parameter label which select the axis tobe affected (Le1=Left one, Le2=Left two, etc.). A table of differentparameters will then be displayed in response to the selection of anaxis. The user then selects the key of the desired new parameter to betrended. A Return key is selected to return to the graph.

The system further permits adjustment of the timescale of the trends toinclude the most interesting parts of the trends. Zoom keys aredisplayed, which, when selected, make it possible to enlarge certainparts of the trend curves. The system is set up so that "zooming" iscentered around the cursor, which can be placed in the middle of theinteresting part of the trend curves by pointing and clicking with themouse. Every time the left "-" zoom button is pressed, the curves aroundthe cursor are expanded. The right "-" zoom button has the reverseeffect; it goes back and shows bigger portions of the curves.

The system also provides a Scale key, which when selected displaysadditional keys which enables the user to adjust the size of thedisplayed graph. The height of the trend graph(s) may be increased ordecreased by selecting arrows under the Max label to the left and to theright of the graph. The baseline offset may be adjusted by selecting thearrows under the Offset label.

After the scales have been changed, they may be reset to default at anytime by pressing the Normal key.

Again, a Return key must be selected to return to the graph. The systemfurther allows the time to be changed with a key displayed on the bottomright hand side. Clock time is the time of day (8:30 means eight thirtyin the morning) while Relative time is time since admission (8:30 meansthat the patient has been monitored for eight and a half hours).

It is also a particular advantage of the system employing the methodthat a number of settings controlling the MIDA analysis may be adjustedto customize the analysis. The MIDA setup is available through the MIDASetup key.

The different settings are described below, one by one. Each group ofsettings may be reset to default values individually by pressing theNormal key next to each group.

The MIDA interval is the time interval within which the MIDA analysiswill produce new values. During each interval, all acquired ECGs ofsufficient signal quality that match the initial reference ECG will beaveraged to form an ECG with improved signal quality. At the end of theinterval, the averaged ECG is used when calculating the MIDA parameters.The averaged ECG and the 5 parameters values of every such interval isstored in the Acquisition Module for approximately 3000 intervals.

Short intervals (less than 1 minute) have the advantages of fastresponse to rapid ECG changes, but they also have more noise and resultin a shorter total recording time. Long intervals (more than 1 minute)have less noise and result in a longer recording time but they alsorespond slowly to rapid ECG changes. Generally, one minute intervals arerecommended for CCU monitoring (infarction, unstable angina, etc.) and15 second intervals are recommended for PTCA use. The default setting ispreferably 1 minute.

To form an averaged ECG at the end of the intervals previouslydescribed, a minimum number of beats must have been included in theaverage. Too low a limit may result in poor signal quality. Too high alimit may result in difficulties reaching the limit with no calculatedparameter values as a result. Naturally, the minimum number of beatsrequired is dependent on the interval length.

Recommended settings:

    ______________________________________                                        MIDA interval    Minimum number of beats                                      ______________________________________                                        10 seconds       1 beat                                                       15 seconds       1 beat                                                       30 seconds       2 beats                                                      1 minute         2 beats (factory setting)                                    2 minutes        10 beats                                                     4 minutes        10 beats                                                     ______________________________________                                    

If the signal quality of the acquired ECG is too poor, the ECG will notbe used for MIDA analysis. This is to avoid false results--artifacts.Each ECG signal has to pass the following tests to be included in theMIDA analysis.

A signal spike is a very short disturbance of considerable signalstrength. The origin of the disturbance may be electromagnetic radiationfrom other equipment, bad lead wires or pacemakers. The spike test maybe turned on or off. When spikes are detected, the MIDA analysis ishalted unless the patient has a pacemaker.

Noise may be caused by many reasons. Bad patient electrode connectionmay be one reason. Line disturbances from other equipment close to thepatient cable may be another. The noise threshold may be set to 5, 10,20, 50 or 100 micV or may be turned off. When excessive noise isdetected, the MIDA analysis is halted. The default setting is 50 μV.

If the baseline variation is too big, this may distort the ECG. Thebaseline threshold may be set to 25, 50, 100, 200 or 400 micV/second orbe turned off. When baseline variation is detected, the MIDA analysis ishalted. The preferred default setting is 100 micV/sec.

The default settings may be selected by the user in a table of defaultsettings which is opened by selecting the System key and entering anaccess code. The table includes a Save key and a Cancel key which, whenselected, respectively set the default settings or close the menu withno alterations to the default settings.

THIRD EMBODIMENT

A third embodiment of the invention may be used as a complement to aconventional monitoring system for enhanced monitoring and documentationof the ECG in terms of ischemia, infarction and arrhythmia.

This embodiment also has the advantages of ischemia monitoring withparameters reflecting the ECG changes in clear trend graphs, averaged12-lead ECG acquisition, storage and display, arrhythmia detection,24-hour full disclosure arrhythmia of all monitored patients, and24-hour continuous 12-lead ECG stored for all monitored patients.

However, this embodiment does not contain a monitoring system withwaveforms and arrhythmia alarms. Rather, it is a system for onlymonitoring ischemia and the course of various heart diseases. Waveformsand alarms are controlled and monitored using the conventionalmonitoring system.

It consists of the elements shown in FIG. 7, except that instead of abedside monitor, it has an Acquisition Module for each patient,connected via Ethernet to a central Server. The server displays andstores data from all connected Acquisition Modules. It is a supplementto a conventional monitoring system adding the functionality describedwith respect to the first embodiment.

The Acquisition Module works in parallel with the patient monitor of theconventional monitoring system. The ECG signal from the patient is fedinto both the Acquisition Module as well as the patient monitor. Theparallel connection is achieved with an adapter cable between theacquisition module and the patient monitor.

The Acquisition Module acquires the signal, converts it from analog todigital and performs ischemia and arrhythmia analysis. The AcquisitionModule communicates with the central Server via an Ethernet connectionon the back. It also includes a serial port for connection to otherdevices, such as the Hewlett Packard VueLink interface module.

FIG. 12 shows a face of an Acquisition Module. Element 121 is an ECGinput for use with either 8-lead or 5-lead patient cables. Element 122is a Signal out for connection to the ECG input of the conventionalmonitor. Element 123 is a graphic depiction of the patient, which inthis case includes only the torso. More or less parts of the patient maybe included in the graphic depiction of the patient, for example, thelimbs. A number LEDs or other light producing means are placed behindthe graphic depiction of the patient, each at positions corresponding tothe electrodes on the patient's body. Each electrode may be indicatedindividually with a twinkling yellow light if the signal quality is pooror with a steady yellow light if the lead fails. When the signal qualityis all right, all electrode indicators are off. Alternatively, theelectrodes may blink at different rates or display different colorsdepending upon the conditions of the electrodes discussed with referenceto the second embodiment. The graphic depiction of the patient may besilk screened, wet painted, powder coated, multi-color molded plastic,or overlay film, for example. Element 124 is a MIDA status indicatorwith a green and yellow indicator. The green indicator is on when MIDAanalysis is running. If the MIDA analysis is not running for anyone ofvarious reasons, the yellow indicator is on. Element 125 is a backposition indicator. A back position sensor is a position sensitivedevice that may be used to record if the patient is lying on his back ornot. This information may be useful when examining the most sensitiveparameters such as QRS-VD of the MIDA analysis. When such a sensor isused, the back position indicator is green only when the patient islying on his back. Element 126 is an event Mark key. When this key ispressed, an event mark is recorded by the system. Element 127 is a Pausekey. The recording may be paused and resumed with this key. When paused,recording and analysis are temporarily halted. This is indicated with ayellow light behind the pause symbol. Element 128 is a Discharge Patientkey. When this key is pressed, the current recording is terminated andthe MIDA module is ready to start a new. Element 129 is a Main Poweroperation indicator. A green light indicates that the module is on,running on main power. Element 130 is a Battery Power operationsindicator. A yellow light indicates (a warning) that the module is on,running on the internal battery for very limited time. Element 120 is anOn/Off Switch. The module is turned on by pressing the switch. Themodule is turned off by pressing the switch again.

The patient input of the MIDA Acquisition Module is of Type CF, it isdefibrillation proof (it may remain connected to the patient duringdefibrillation), and the patient connector on the front is marked withthe appropriate heart symbol.

The patient input of the MIDA Acquisition Module is designed to limitthe current through the patient to a few microAmperes and to comply withthe requirements for low leakage currents when connected to aconventional Monitoring System. If other equipment than the MIDAAcquisition Module is connected to the patient, it should beinterconnected with an equipotential grounding cable. On the back of theMIDA Acquisition Module there is an equipotential grounding terminal forthis purpose. The following connections are provided on the rear (notshown) of the MIDA Acquisition Module:

AC in--to be connected to a grounded electrical AC source of 100-240V+-10% , 50-60 Hz.

Equipotential grounding terminal--used to obtain the same electricalearth reference when additional electrical equipment is used togetherwith the MIDA Acquisition Module.

Ethernet--for connection to the Ethernet network.

RS-232 Serial communication--for connection to other devices, such as aHewlett Packard VueLink module.

The Acquisition Module is equipped with an internal battery that isswitched in as soon as the AC power is insufficient. The internalbattery provides full operation for at least five minutes, when fullycharged. When the MIDA Acquisition Module operates on the internalbattery, a yellow LED is lit in the lower right corner of the front,under the battery symbol. The internal battery is recharged as soon asthe AC power is back and the Module is on. Line power operation isindicated by a green LED in the lower right corner, under the AC symbol.

Workstation 11 also contains a 17"color monitor on which curves and datafrom one patient at one time may be brought up for examination. Theworkstation also contains a graphical interface with a mouse, which maybe used to control the operation of up to two of the central monitoringunits. However, the central monitors are not disturbed at all when themonitoring of one specific patient is controlled or examined at theworkstation. All information presented on the workstation at any timemay be printed on the laser printer.

A row of keys on the top of the workstation monitor allows 5 selectionand direct control of the monitoring of each patient. The keys aremarked with an identification tag for each bed (normally 1, 2, 3 and soon). When a patient has been selected, the operator may controladmission/discharge, alarm settings, waveforms monitored, and much morein a straightforward and easy manner using the graphical interface. Amonitoring session may also be examined in detail in terms of ischemia,12-lead ECGs and full disclosure arrhythmias.

When the ischemia trends are examined on the workstation, any one of 30different calculated parameters may be examined over time. Interestingevents may then be expanded on the screen and exact values correspondingto the events will be shown. Short events can be expanded to display acouple of minutes on the display even if the entire trend covers severaldays of monitoring.

The system in the preferred embodiment of the invention reduces the needfor additional 12-lead ECGS. Minute-by-minute, derived 12-lead ECGs areautomatically acquired and stored in the system. Several 12-lead ECGsmay be superimposed from different times in order to plot gradualchanges. By pointing out interesting ischemic events in the ischemiagraphs, the corresponding 12-lead ECGs may be displayed, superimposed orprinted on the laser printer, if desired. Thus the morphologic nature ofthe ischemic changes may be examined in real time, i.e., duringthrombolytic therapy or unstable angina.

Workstation 11 also contains a complete 24-hour full disclosurearrhythmia review function. The arrhythmia graph is presented on thelower half of the workstation display, with the arrhythmias plotted ascolored dots or lines depending on the duration of the arrhythmias. Thecorresponding ECG is displayed on the upper half of the display. Everysingle heartbeat during the previous 24 hours can be displayed for eachmonitored patient by pointing out either the arrhythmia of interest orthe desired time of day.

The system also contains a data storage unit for storing all data fromthe monitoring session for future examination. A stored recording may beexamined on the workstation in exactly the same way as currentlymonitored patients.

The preferred embodiment of the invention described above uses acomplete networking system for a number of patients to perform thefollowing analysis and monitoring. However, this method of analysis andmonitoring may be technically implemented using different hardware,system architecture or a special program code in a different programcoding. The method may, for example, be used in a stand-alone system fora single patient.

The method may also be used in an ambulatory application. In such anapplication, ECG signals are recorded over a long period of time by arecording device worn or carried by the patient. The recorded signalsare later retrieved for printout and analysis. The signals may then beanalyzed according to the method described here below.

In a telemetry application, the patient carries a small transmitterwhich transmits the ECG signals to a receiver where the signals aredisplayed in real time. The ECG signals received by the telemetry systemare then analyzed according to the following method.

The invention is not limited to the systems and methods illustrated inthe drawings and described above. Modifications and variations arepossible within the inventive concept. For example, in addition to theelectrode leadsets discussed above, the following leadsets may be used:the 3-lead electrode leadsets of FIGS. 16, 17, and 18, the 4-leadelectrode leadsets of Figs. 19 and 20, the 5-lead electrode leadsets ofFIGS. 21, 22, and 23 (the EASI leadset and algorithm of FIG. 23 arecovered by U.S. Pat. No. 4,850,370, Issued Jul. 25, 1989), the 7-leadelectrode leadset of FIG. 24, the 8-lead electrode leadset of FIG. 25according to Frank, and the 10-lead electrode leadset of FIG. 26. Inaddition, body surface mapping (normally with 48 electrodes) may beapplied to the invention. Accordingly, the disclosure should not beconstrued as limiting the scope of the following claims, whichspecifically define the invention.

What is claimed is:
 1. A system for monitoring, analyzing, and/or diagnosing the cardiac activity of a patient, comprising:plurality of electrodes positioned at a respective plurality of locations on the patient for directing a respective plurality of electrical signals from the patient; ECG data production means connected to the plurality of electrodes for acquiring said plurality of electrical signals directed by the plurality of electrodes and for producing ECG data in response to the acquired electrical signals; display means connected to the ECG data production means for displaying a graphic depiction of at least part of the patient, the location, on the graphic depiction of at least part of the patient, of each of said plurality of electrodes, and a status of each of said electrical signals directed from said plurality of electrodes, wherein the status of each of said electrical signals directed from each of said plurality of electrodes includes at least one condition in which the electrical signal has a value such that the ECG production means is unable to produce a valid ECG signal in response thereto.
 2. The system of claim 1, wherein said display means includes a plurality of electrode status indicators, each of said plurality of electrode status indicators being disposed on the graphical depiction of at least part of the patient at a position substantially corresponding to one of said plurality of locations on the patient at which one of said plurality of electrodes is positioned.
 3. The system of claim 2, wherein said display means includes a plurality of electrode status annunciators, each of said plurality of electrode status annunciators being alphanumeric indicators and corresponding to at least one of said electrode status indicators.
 4. The system of claim 3, wherein the status of each of said plurality of electrical signals directed from each of the plurality of electrodes further includes a first condition in which the electrical signal is out of the acquisition range of the ECG production means, a second condition in which the electrical signal is too noisy for the ECG production means to produce a proper ECG signal in response thereto, a third condition in which the electrical signal exhibits baseline drift, and a fourth condition in which the signal exhibits a spike, wherein each of said plurality of electrode status indicators produces a graphic output when the electrical signal corresponding thereto is in one of the first, second, third, or fourth conditions and each of said electrode status annunciators indicates which of said conditions the corresponding electrical signal is in.
 5. The system of claim 4, wherein each of said electrode status annunciators is adapted to selectively display an impedance value of at least one of said plurality of electrodes.
 6. The system of claim 2, wherein the status of each of said plurality of electrical signals directed from each of the plurality of electrodes further includes a first condition in which the electrical signal is out of the acquisition range of the ECG production means and a second condition in which the electrical signal is too noisy for the ECG production means to produce a proper ECG signal in response thereto, wherein each of said plurality of electrode status indicators produces a first graphic output when the electrical signal corresponding thereto is in the first condition and each of said electrode status indicators produces a second graphic output when the electrical signal corresponding thereto is in the second condition.
 7. The system of claim 2, wherein said display means comprises a cathode ray tube.
 8. The system of claim 2, wherein said display means comprises a plasma display.
 9. The system of claim 2, wherein said display means comprises a liquid crystal display.
 10. The system of claim 2, wherein said display means comprises an electroluminescent display.
 11. The system of claim 1, wherein said display means includes a translucent overlay having a graphical depiction of at least part of the patient and a plurality of light production means disposed behind the translucent overlay, each of said plurality of light production means being disposed behind the transparent overlay at a position substantially corresponding to one of said plurality of locations on the patient at which one of said plurality of electrodes is positioned.
 12. The system of claim 11, wherein each of said plurality of light production means is a light emitting diode.
 13. The system of claim 12, wherein the status of each of said plurality of electrical signals directed from each of the plurality of electrodes further includes a first condition in which the electrical signal is out of the acquisition range of the ECG production means and a second condition in which the electrical signal is too noisy for the ECG production means to produce a proper ECG signal in response thereto, wherein each of said light emitting diodes produces a first light output when the electrical signal corresponding thereto is in the first condition and each of said light emitting diodes produces a second light output when the electrical signal corresponding thereto is in the second condition.
 14. A method for monitoring, analyzing, and/or diagnosing the cardiac activity of a patient, comprising:positioning a plurality of electrodes at a respective plurality of locations on the patient for directing a respective plurality of electrical signals from the patient; acquiring said plurality of electrical signals by connecting ECG data production means to the plurality of electrodes; producing ECG data in response to the acquired electrical signals; and displaying on display means connected to the ECG production means the location, on the patient, of each of said plurality of electrodes and a status of each of said electrical signals, wherein the status of each of said electrical signal has a value such that the ECG data production means is unable to produce a valid ECG signal in response thereto.
 15. The method of claim 14, wherein said display means includes a graphical depiction of at least part of the patient and a plurality of electrode status indicators, each of said plurality of electrode status indicators being disposed on the graphical depiction of at least part of the patient at a position substantially corresponding to one of said plurality of locations on the patient at which one of said plurality of electrodes is positioned.
 16. The method of claim 15, wherein said display means includes a plurality of electrode status annunciators, each of said plurality of electrode status annunciators being alphanumeric indicators and corresponding to at least one of said electrode status indicators.
 17. The method of claim 16, wherein the status of each of said plurality of electrical signals directed from each of the plurality of electrodes further includes a first condition in which the electrical signal is out of the acquisition range of the ECG production means, a second condition in which the electrical signal is too noisy for the ECG production means to produce a proper ECG signal in response thereto, a third condition in which the electrical signal exhibits baseline drift, and a fourth condition in which the signal exhibits a spike, wherein each of said plurality of electrode status indicators produces a graphic output when the electrical signal corresponding thereto is in one of the first, second, third, or fourth conditions and each of said electrode status annunciators indicates which of said conditions the corresponding electrical signal is in.
 18. The method of claim 15, wherein the status of each of said plurality of electrical signals further includes a first condition in which the electrical signal is out of the acquisition range of the ECG production means and a second condition in which the electrical signal is too noisy for the ECG production means to produce a proper ECG signal in response thereto, wherein each of said plurality of electrode status indicators produces a first graphic output when the electrical signal corresponding thereto is in the first condition and each of said electrode status indicators produces a second graphic output when the electrical signal corresponding thereto is in the second condition.
 19. The method of claim 14, wherein said display means includes a translucent overlay having a graphical depiction of at least part of the patient and a plurality of light production means disposed behind the translucent overlay, each of said plurality of light production means being disposed behind the transparent overlay at a position substantially corresponding to one of said plurality of locations on the patient at which one of said plurality of electrodes is positioned.
 20. The method of claim 19, wherein each of said plurality of light production means is a light emitting diode.
 21. The method of claim 20, wherein the status of each of said plurality of electrical signals further includes a first condition in which the electrical signal is out of the acquisition range of the ECG production means and a second condition in which the electrical signal is too noisy for the ECG production means to produce a proper ECG signal in response thereto, wherein each of said light emitting diodes produces a steady light output when the electrical signal corresponding thereto is in the first condition and each of said light emitting diodes produces a blinking light output when the electrical signal corresponding thereto is in the second condition. 